Delicately Controlled Polymer Orientation for High-Performance Non-Fullerene Solar Cells with Halogen-Free Solvent Processing

Abstract

Molecular orientation in polymer solar cells (PSCs) is a critical subject of investigation that promotes the quality of bulk heterojunction morphology and power conversion efficiency (PCE). Herein, the intrinsic polymer orientation transition can be found upon delicate control over the branching point position of the irregular alkoxy side chain in difluoroquinoxaline−thiophene-based conjugated polymers. Three polymers with branching points at the third, fourth, and fifth positions away from the backbone were synthesized and abbreviated as PHT3, PHT4, and PHT5, respectively. Temperature-dependent absorption behavior manifests the polymer aggregation ability in the order of PHT3 < PHT4 < PHT5. Surprisingly, the polymer orientation transition from typical face-on to edgeon emerged between PHT4 and PHT5, as evidenced by X-ray-scattering analysis. The enhanced face-on crystallinity of PHT4 endowed the o-xyleneprocessed PHT4:IT-4Cl-based devices with the highest PCE of 13.40%. For PHT5 with stronger aggregation, the related o-xylene-processed PSCs still showed a good PCE of 12.66%. Our results demonstrate that a delicate polymer orientation transition could be realized through a precisely controlled strategy of the side chain, yielding green-solvent-processed high-performance PSCs.

Fine‐Tuning of Siloxane Pendant Distance for Achieving Highly Efficient Eco‐Friendly Nonfullerene Solar Cells

“…Previous reports have confirmed that relative to alkyl group, the siloxane terminal possesses lower surface energy property. Although the contents of the siloxane terminal in PQSi505, PQSi705, and PQSi905 are the same (5 %), the result suggests a longer linker in the polymer would result in a lower surface energy [6c,12] . In this regard, the siloxane terminal group is a powerful modulator to regulate surface property.…”

“…Our result indicates that the slight branching position change of siloxane‐terminated group can greatly influence the orientation and crystallinity features. Thus, the siloxane pendant can be regarded as a powerful hybrid functional group, considering the extremely low molar content of the siloxane‐terminated side chain (5 %) in the polymers [5a,6c,13] . Generally, conjugated polymers with high crystallinity would exhibit outstanding charge transport.…”

“…The innovative research on siloxane‐terminated side chain stemmed from the modification of isoindigo‐based polymer toward high‐mobility organic field‐effect transistor [9a] and then extended to other donor–acceptor‐type conjugated polymers. The introduction of siloxane groups could influence polymer aggregation and crystallinity and induce significant orientation transition for polymers [6c,9c,10] . Recently, the powerful effect of siloxane‐terminated side chain on polymer property and blend morphology has been further confirmed by our group [10a] through a minor combinatory side chain approach, which stimulated us to search for deeper insight into the critical role of siloxane pendant.…”

Advances in the device design and printing technology for eco-friendly organic photovoltaics

“…Appropriate pre-aggregation is recognized as a prerequisite for achieving high-quality active layer films. [67][68][69] Cao et al 70 revealed that the polymer donor PTzBI and acceptor N2200 exhibited strong intrinsic pre-aggregation in 2-methyltetrahydrofuran (Me-THF) solvent. Such pre-aggregation contributes to the formation of interpenetrating network structures with small domains and high domain purity (Fig.…”

Impact of Chemical Design on the Molecular Orientation of Conjugated Donor–Acceptor Polymers for Field-Effect Transistors

“…Several other nonfullerene acceptors such as tetrachlorinated IT-4Cl, 97 perylene bisimide-based SdiPBI-Se, 98 and fused dithienothiophen[3,2-b]-pyrrolobenzotriazole-(BTA-core-) based Y14 99 were also capable of influencing the packing orientation of donor polymers. The extended conjugation of such acceptors significantly enhanced their interaction with conjugated polymers (donor), efficiently tuning the polymer packing orientation.…”